1. Field of the Invention
This Invention relates to a worm gear and, more specifically, to an improved worm wheel having a removable wear member mounted thereon between the wheel and the worm.
2. Description of the Prior Art
In a worm gear including a worm and worm wheel it has been found desirable to provide a self-lubricating surface such as plastic or polytetrafluoroethylene. However, in many instances, a worm or wheel made entirely of this substance would not satisfy the operational strength requirements.
Further, it has generally been a problem when selecting a base material of the worm or wheel that any significant wear would require the entire member to be replaced in order to provide continued effective operation.
Accordingly, it has been taught in the past that an outer surface portion of a power drive member might be removably secured thereto for subsequent replacement of just the outer portion after excessive wear. U.S. Pat. Nos. 519,781 and 601,990 and early patents regarding sprocket wheels disclose this general concept. They present, however, relatively complicated means for securing the outer portion to the base power drive member preventing them from being applicable in many cases.
More recent efforts, such as those disclosed in U.S. Pat. Nos. 2,923,166 and 3,059,491 recognize the desirability of using two different materials within the power drive member and also in providing a means for replacing only the outer portion when it becomes extensively altered by wear. U.S. Pat. No. 3,059,491 further teaches that it is desirable for the wear to occur at the outer portion to prevent wear and subsequent replacement of the power drive member and the mating power transfer member which are generally more expensive to replace.
However, nothing is taught in nor suggested by these prior art devices to indicate that this wear concept can be utilized in a worm gear. The wear portions disclosed therein are either tightly fitted about the power drive member or complicatedly attached thereto.